1. Field of the Invention
The present invention generally relates to an optical disk drive such as a CD-ROM drive, and more particularly to a method for controlling the number of disk revolutions in an optical disk drive during a data-read operation.
2. Description of the Related Art
A well-known rotation control system used in disk drives adapted to drive an optical disk is a constant angular velocity (CAV) system in which data is read out from a disk in a constant number of disk revolutions. Another well-known rotation control system used in disk drives, is the constant linear velocity (CLV) system, where the number of disk revolutions is controlled to allow the transfer rate (i.e., Bits Per Second) of read-out data to be constant.
In optical disk drives using the CLV system, the number of disk revolutions must be controlled along with a control for the position of a pick-up when data access is carried out in accordance with a command from a host computer. As a result, an increase in mechanical load is involved. It is also difficult to achieve high-speed access using CLV systems. For this reason, a number of alternative rotation control systems have been used in optical disk drives such as CD-ROM drives, in place of the conventional CLV system.
In conventional CLV systems, in which rotation control is monitored in each data zone of the disk, velocity signal information is typically required. To generate such velocity signal information, synchronization signals are used which are recorded on the disk in the form of pit signals. When the rotating velocity of the disk comes into a range where reproduction of synchronization signals is enabled, a synchronization signal is accurately reproduced by a start-up circuit. In conventional CLV control systems, a phase locked loop (PLL) control based on an accurately reproduced synchronization signal may be used. That is, disk rotation can be controlled in a conventional CLV system by PLL-locking disk data in accordance with a velocity signal extracted from read-out data.
In conventional zone CLV control systems, however, the number of disk revolutions varies in a non-sequential manner between neighboring zones. In other words, the number of disk revolutions varies abruptly at the boundary between neighboring zones. For this reason, when the data read-out position is shifted from a zone to a neighboring zone during a sequential data read-out operation, read-out errors may be generated due to the abrupt variation in the number of disk revolutions occurring at the boundary between the two zones. Where successive data recorded over two zones on the disk is read out, a processor for performing servo control (i.e., a disk motor servo) detects a difference between the target number of disk revolutions and the actual number of disk revolutions at a point in time when the position for reading out the data is shifted from one of the zones to the other zone beyond the boundary therebetween. In this state, accordingly, the disk motor should be abruptly accelerated until the actual number of disk revolutions reaches the target number of disk revolutions. This results in an abrupt variation in the rotation of the disk, thereby resulting in an erroneous PLL lock. As a result, read-out errors may be generated.
This tendency to generate read-out errors may increase where the interval of each zone is increased. This is due to an increased variation in the number of disk revolutions. Where a reduced zone interval is used to solve this problem, another problem occurs in that there is a limitation in terms of hardware. For example, there is a limitation whereby the oscillation frequency of the disk drive""s clock generator is susceptible to variations from unit to unit.
According to the present invention, as embodied and broadly described herein, a zone CLV control system divides the disk data recording region into a plurality of zones where independent CLV control is carried out in each respective zone. This system is comparable to a conventional CLV control system in which sequential rotation control is carried out over the entire region of the disk (i.e., between the inner and outer peripheries) in order to obtain a constant data transfer rate over the entire region of the disk. The present invention, however, differs from conventional zone CLV rotation control in that the control of the disk rotation is carried out independently in each respective zone thereby effectively preventing the generation of data read-out errors.
In accordance with one aspect, the present invention provides a method for controlling the number of disk revolutions in each zone of an optical disk drive having a data region divided into a plurality of zones comprising the steps of: determining whether or not a zone change occurs during a read-out of sequential data; and attenuating a gain of a rotation control system for a disk motor when it is determined that there is a zone change.
In accordance with another aspect of the present invention, a method is provided for controlling the number of disk revolutions in each zone of an optical disk drive having a data region divided into a plurality of zones comprising the steps of: determining whether or not data to be read out is sequential data, when a zone change occurs; and attenuating a gain of a rotation control system for a disk motor when it is determined that the data to be read out is sequential data and then executing a zone change. When it is determined that the data to be read out is not sequential data, the gain of the disk motor rotation control system is increased. Under this condition, a seek operation is executed.
The zone CLV control system of the present invention provides advantages over conventional CLV control systems in the reduction in the mechanical load such as the amount of heat generated from the spindle motor. This occurs because the variation in the number of disk revolutions is relatively small, thereby resulting in a reduction in the rotation control range.